Comte de MonteCristo vs. Kasparov

Continuing with the third section of Recent Comments Near and Far, Comte de MonteCristo wrote,

Mark Weeks writes that "Kasparov slipped on his 20th move" which is 20.Nxe8 capturing the knight. I do not know what move Weeks has in mind at move 20. I think 90% of chess players would play 20.Nxc8 capturing the bishop for a knight on the general principle that bishops are better than knights in relatively open endgames. Nevertheless, I have come to the conclusion that 20.Nxc8 only achieves equality and that Kasparov's surprising 20.Nxe8 wins the game and is exactly the right move!

The following diagram shows the position.

Moscow 1985 (game 1)
Karpov, Anatoly

Kasparov, Garry
(After 19...Nc7-e8)
[FEN "1rbrn3/p2pkppp/1p1Np3/2P5/1RPP4/6P1/P3KPBP/7R w - - 0 20"]

I was initially alerted to this position by IM (now GM) Jonathan Tisdall, who reported on the match in the December 1985 issue of Chess Life (p.28). Kasparov played 20.Nxe8, and Tisdall commented, 'As Kasparov pointed out after the game, he should have played 20.Nxc8+, preserving all the advantages of his position and soon forcing the win of the b-Pawn. Karpov now has defensive chances.' In his book on the match, Kasparov gave a deeper explanation.

The plausible continuation proves not to be the best. A concrete approach to the position would have suggested to White the unobvious exchange of his fine Knight for the Bishop which has not made a single move. 20.Nxc8+! Rbxc8 (20...Rdxc8 21.Rhb1 and 22.Kd3) 21.cxb6 axb6 22.Kd3 Nd6 23.Rc1 Rb8 24.Rcb1 Rbc8 (24...Rdc8 25.a4 -- 26.a5) 25.Ra4 Rb8 26.Ra6 Rdc8 27.Rb4, and Black is lost.

Karpov responded 20...Kxe8. Tisdall: 'Black could have had decent drawing chances by 20...Rxe8 21.Rhb1 Ba6 22.Ke3 Rec8. White gets nowhere after either 23.c6 Rc7 or 23.Bf1 e5! 24.cxb6 Rxb6 25.Rxb6 axb6 26.Rxb6 Bxc4 27.Bxc4 Rxc4 28. dxe5 Ra4. Kasparov gave a different variation:

Black promptly returns the compliment. Another possibility of exploiting the King's position at e2 would have been given by 20...Rxe8! 21.Rhb1 Bb7 22.d5 exd5 23.cxd5 Kf8+ 24.Kd2 Ra8, with fair chances of saving the draw.

Kasparov's 21...Bb7 does seem stronger than Tisdall's 21...Ba6. The game continued 21.Rhb1 Ba6 22.Ke3 d5 23.cxd6 Rbc8 24.Kd3 (according to Kasparov, a little better is 24.Ra4) and Black resigned on the 42nd move. To play through the complete game see...

Garry Kasparov vs Anatoli Karpov, World Championship Match 1985
http://www.chessgames.com/perl/chessgame?gid=1067186

...on Chessgames.com.